A pipe joint structure for coupling a first pipe member and a second pipe member is for example disclosed in Japanese Unexamined Patent Publication No. 2004-183703. The pipe joint structure uses a pipe joint for joining a male joint portion of the first pipe member and a female joint portion of the second pipe member. The pipe joint includes a cylindrical body formed with a pair of slits extending from one end of the cylindrical body in an axial direction. The pair of slits are opposed to each other with respect to an axis of the cylindrical body. Also, the cylindrical body is formed with engaging portions at axial ends thereof. The engaging portions project in a radially inward direction.
The pipe joint is mounted to one of the first and second pipe members, and then the other one of the first and second pipe members is coupled thereto. An axially middle portion of the cylindrical body, between the engaging portions, is thinner than the engaging portions and is deformable to allow displacement of the engaging portion in a radial direction. Thus, the engaging portion is capable of expanding and contracting in the radial direction when coupled to the other one of the first and second pipe members.
In this pipe joint structure, however, in a condition that the first and second pipe members are filled with an internal fluid such as refrigerant, the pipe joint receives a force in a direction to separate the first and second pipe members. It was found that the axially middle portion of the pipe joint particularly receives a compression force due to the internal pressure.
When a modulus of section of the thin axially middle portion reduces, the axially middle portion is likely to cause compression buckling and to be deformed. Further, if the first and second pipe members are affected by a pulling force due to external stress such as vibration of a vehicle, the axially middle portion receives the compression force due to the pulling force. In addition, when the pipe joint is located radially outside of the first and second pipe members, an external form of the coupling portion increases.